We humans like to put things into neat, little boxes. Naming, labeling, categorizing, classifying: it’s normal, but can easily confuse us when the process goes awry. What if something is on the edge of one category versus another; teetering on the cusp of one state of being before plunging into another? That challenges our desire for static status, and can make things more confusing.

Isn’t that weird? When I first saw it I thought it was a planetary nebula; the (poorly-named) structure that forms around a dying star. As stars age, their cores shrink and heat up. Through complicated physics, they wind up blowing off a dense stream of particles like a solar wind. There can be several stages to this process, but it ends with the star totally ejecting its outer layers, exposing its tiny, über-dense but incredibly hot core, surrounded by eerily-shaped clouds of gas glowing due to the ultraviolet light from the exposed core.

But I was wrong: it’s not a planetary nebula, but a proto-planetary nebula. That is, the star is blowing that wind, enveloping itself in clouds of gas, but the core is not yet hot enough to make the gas itself glow on its own like a fluorescent light bulb. Instead, the gas is merely reflecting the light from the star. I know that doesn’t sound like much of a difference, but it really is. The physics of how and why this object gives off light is very different, for one. This image here is in two colors; the kind of light we see (visible light) which is tinted blue in the picture, and infrared light (falsely colored red in the picture). Usually, planetary nebula are faint in the IR, but this one is quite bright in that light; the gas itself doesn’t emit much IR, but the star sure does, and the gas is reflecting it.

Normal planetaries tend to glow green due to the presence of atomic oxygen; it emits very strongly in that part of the spectrum. But again, the star here doesn’t have enough oomph to get that process going, so the gas just sits there. It looks like a planetary nebula to me, but only kinda sorta. The shape is right, but the essence of it is not.

The shape is really weird, too. We see lots of planetaries like this, but still. A star all alone in space would normally emit gas in a rough sphere around itself, but in this case something is shaping the wind. Most likely it’s some sort of companion: a star orbiting very close in, perhaps. Or, it’s possible that the star we see here had planets, and as it died it expanded, engulfing those planets. As they orbited inside the star, frying the whole time, they would help accelerate the star’s spin. That too could produce the wonderful bipolar shape of the gas around the star.

We’re not precisely sure how objects like this evolve; how they get their start, how they get their structure, and how they eventually turn into a full-fledged planetary nebula. Stars don’t stay in this stage for long, so finding one is a rare opportunity to learn more about them and get answers to those questions. Sometime in near future — a few thousand years, perhaps — as the star gets hotter, it will eventually reach that special moment when it starts to blast out ultraviolet light. At that point it will have the power needed to make the gas glow, and IRAS 13208-602 will become a real planetary nebula, joining hundreds of others we know about.

Until then, it sits in its own box, or perhaps on the lip of two. Only time will be able to tip it from one to the other.

A proto-planetary DISK is, last I heard, the disk of material around a newly-formed star that’s in the process of cendensing out into planets. So, when I’ve said “proto-planetary nebula” in the past, I’ve meant the gas cloud around a really young star (or protostar) that has yet to condense out into planets or a proto-planetary disk.

So I now have to be careful when talking about a “proto-planetary … nebula” (a nebula around a protostar that will eventually form planets), versus a “proto … planetary nebula” (the halo around a dying star that will eventually become a planetary nebula).

I’ve always wondered, what’s the upper mass limit for a star to eject a planetary nebula? At what point do stars transition from ‘planetary nebula’ to ‘Wolf-Rayet star followed by an Earth-shattering kaboom’? (At least I thought that that was the order of things?)
And as is the topic of discussion here, what happens right on the cusp (of supernova)?

Of course, I may be utterly ignorant of stellar evolution, so feel free to correct, as always…
@8 John Moore: Wait, what?

@ Cryptoknight: If it WAS a Niven ring, I feel sorry for the poor mofos who got cooked… But then, a species that could actually build something like that would probably just fling it off into space in search of a younger star – think of it as an insterstellar mid-life crisis 😉

In the distance, at about 8 o’clock from the star itself, nicely lined up with its left-pointing cone, is what looks like a pair of clumpy jets emanating from another star.

If that’s just a leading wisp of IRAS 13208-6020’s emissions, it’s quite a coincidence that it lines up symmetrically with the other star. If it’s another star blowing off jets, it’s still quite a coincidence to get two of them in the same frame.

While we’re at it, can’t astronomers come up with a new name for this phenomenon? The term ‘Planetary Nebula’ itself was coined in the 18th century due to the resemblance of some round PN to planets through small telescopes. It’d be as if we still used the term “horseless carriage” to describe cars. And don’t tell me the scientific community can’t do it! They turned both Pluto, previously a planet, and Ceres, previously an asteroid, into Dwarf Planets in one fell swoop.

Phil, this is a terrfic opportunity to call attention to a long-standing pet peave of mine regarding the miserably antiquated term, “planetary nebula”. For decades I’ve tried to get astronomers initerested in upgrading that awful name and using one that makes sense. It has probably been responsible for more misunderstandings and more wasted effort in the form of unlrelentingly repeated corrective print and explanation in everything from news articles to text books in the classroom over the best part of the last century than any other single astrophysical term (The typical example: “Planetary Nebulas”, despite their name, have nothing to do with planets”).

Action is long LONG overdue. My proposal (since the mid-seventies) has been to switch from the explicitly misleading “Planetary Nebula” to “Stellar Terminal Nebula” (STNs), or simply “Terminal Nebula” for short.

Unfortunately, despite my efforts very little interest has been given to it by professional astronomers. Most found it unnecesary. In the 70s and 80s, many thought it would present a big potential for confusion to link a new term with the old one which has held fast in the research literature for generations. Some derided it as “cute” but preferred the conventional term because they grew up with it, that there is history and tradition in it (sounds more like religious dogma to me) or simply because they “liked it” better than my alternative.

You’ve posted here a perfect example of why this issue is so important. It was inevitable that objects that resemble ‘planetary nebula’ (that have nothing whatsoever to do with planets) would inevitably emerge that DO VERY MUCH have to do with planets (like IRAS 13208-6020 – and there are scores of others identified, especially since the HST began its observations).

I’d like to know how many readers here would agree to get rid of this antique astro-scourge once and for all and replace it with a term that makes sense and won’t turn youngsters off on astronomy because they discover that astronomy can be confusing. My old nomination for “Stellar Terminal Nebulae” (STSNs) still stands, l but if anyone came up with a better one, fine. As long as we get rid of ‘Planetary Nebula’.

The objection that changing the name of something causes confusion when looking at older research papers holds no water at all. The IAU seriously needs to get itself an equivalent of the IUPAC nomenclature committee (IUPAC = International Union for Pure and Applied Chemistry). IUPAC have systematised chemical nomenclature and removed a great deal of the confusion that used to exist. Hey, they even changed the carbon-atom numbering system for steroid molecules between me writing my thesis and having my viva!

I can’t (off the cuff) think of anything better than Terminal Nebula as a replacement term.

@ Joseph G (17) – Don’t forget that Ceres also had a turn at being a planet, albeit rather shorter than Pluto’s.

Vesta, Pallas and Juno were also classed as planets briefly – and it might be that at least Vesta becomes a “dwarf planet” – or in my view “planet” full stop – as well.

@ 17. Joseph G :

While we’re at it, can’t astronomers come up with a new name for this phenomenon? The term ‘Planetary Nebula’ itself was coined in the 18th century due to the resemblance of some round PN to planets through small telescopes. It’d be as if we still used the term “horseless carriage” to describe cars.

Or more pertinantly still used the term “spiral nebulae” instead of galaxies! 😉

(I like the old “island universes” term for the galaxies too.)

And don’t tell me the scientific community can’t do it! They turned both Pluto, previously a planet, and Ceres, previously an asteroid, into Dwarf Planets in one fell swoop./I’ll be in the AngryDome if anyone needs me.

Don’t even get me started on the fractal wrongness of that particular piece of IAU stupidity. :-I

Also confusing is that a main-sequence spectral class A star could also be termed “white dwarf” and an F-class one a “yellow-white” dwarf – I think the terms “Sirian” and “Procyonese” respectively fit much better. 😉

@20. Anchor :

I’d like to know how many readers here would agree to get rid of this antique astro-scourge once and for all and replace it with a term that makes sense and won’t turn youngsters off on astronomy because they discover that astronomy can be confusing. My old nomination for “Stellar Terminal Nebulae” (STSNs) still stands, l but if anyone came up with a better one, fine. As long as we get rid of ‘Planetary Nebula’.

I’d support that change in terminology. I’d also very much like to see Uranus be more correctly renamed (re-spelled really) as Ouranos and I’d certainly love to see the IAU’s absurdly mistaken definition of “planet” rectified restoring the “dwarf planets” to being a *class* of planet rather than excluding them from planetary rankings.

Common usage and public understanding does carry some weight methinks and hopes. I suggest we start using the words and seeing if we can get a shift happening.

As for alternatives to “planetary nebula” I’m going to suggest “Ejstellats” from “Ejected Stellar Atmospheres” if we can add to the list of options. This sounds good, indicates their true nature and follows from the traditions model of Pulsar, quasar and Antares. “Protoplanetary nebulae” would then become “Proto-Ejstellats” in turn. Thoughts?

“@ Joseph G (17) – Don’t forget that Ceres also had a turn at being a planet, albeit rather shorter than Pluto’s.”
Vesta, Pallas and Juno were also classed as planets briefly – and it might be that at least Vesta becomes a “dwarf planet” – or in my view “planet” full stop – as well.

Ceres~wise, Isaac Asimov had this to say on its classification :

“… he had left out a planet. It was not his fault; everyone leaves it out. I leave it out myself when I list the nine planets, because it is the four-and-a-halfth planet. I’m referring to Ceres; a small but respectable world that doesn’t deserve the neglect it receives.”
– Page 63, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by
Isaac Asimov, Mercury Press, 1973.

Which I agree with completely.

The smaller worlds – the “ice dwarf planets” to go with the gas giants and rocky “terrestrial” dwarfs – are fascinating heavenly bodies with much of interest and deserve far more respect and higher ranking than they get. Not just Ceres but Pluto, Eris, Sedna and others.

Looks like a specal fx from a scifi movie . Speaking of planetary nebulas I got a good view of the Ring nebula.Nemo we don’t have the tecnogly for the Bussard ramjet now but I think we will some day,this would be increadable .Also I think we will have the Photon sail these two will take us to the stars.

@20 Anchor: Glad to hear that this isn’t just some cranky pet peeve of mine. You put it muh better thab I, and I’m surprised o hear of that level of inertia in the community.
I like Stellar Terminal Nebula, but if I might nitpick, stars aren’t exactly terminated during the process, are they?
I guess that depends on whether a white dwarf is considered a star or a remnant.
Main Sequence Departure Nebulae? Hmm. ‘The Artifact Formerly Known as Planetary’?

@26 MTU: Or more pertinantly still used the term “spiral nebulae” instead of galaxies!
Exactly! Can’t forget that one. And I agree on the stellar dwarf classification thing, too. That one confused the hell out of me, briefly, when I was younger.

I’m not seeing a nebula here at all, we have a singular perspective on this image and no time-based images to follow up. This angle is amazing, though. I see two possibilities, the star we are looking at is spinning perpendicular to the ejecta and had a major hiccup with the south pole at the left and north to the upper right . Higher speed ejecta is not as visable at the received or photographed spectra, but I’m not liking this possibility.

How about this: The star was hit by a medium (stellar) object in line with the ejecta, not enough to disrupt the primary but enough to cause a major ripple in its gas and electro-magnetic output, which could cause the viewed tubular formation in this photo. The direction of the hit would most likely have been from the lower left of the photo, which seems to be directed more toward us than the upper left, and has a more turbulent form at the extreme end of the visible formation.

Here’s another one of these, angled at maybe 50 degrees off of broadside. The explanation is still of the “we don’t know what does it” type, willfully ignoring electrical explanations (see my #24 above). I don’t think collisions are a viable explanation, due to the infinitesimal chances of them occurring – we see too many of these hourglasses. Don’t forget the gravity-only guys are claiming entire galaxies can pass through each other without stellar collisions, only gas-cloud collisions. http://apod.nasa.gov/apod/ap110807.html